Aligning sustainability and regional earthquake hazard mitigation planning: integrating greenhouse gas emissions and vertical equity

Concerns about the potential economic consequences of earthquakes have increased in recent years as scientifically based probabilities of future earthquakes in many large urban areas have risen. These hazards disproportionately impact low-income communities as wealth disparities limit their capacity to prepare and recover from potentially disastrous events. In addition to major economic losses, the activities related to building recovery result in significant greenhouse gas emissions contributing to climate change. This article develops a framework that quantifies the complex relationships between pre-earthquake retrofit activities and their economic, environmental and equity implications to promote informed decision-making, using the city of San Francisco, California as a case study. This research consists of two sections. In the first section, a bi-objective optimization model is proposed to identify optimal earthquake risk mitigation policies to minimize total earthquake-related economic and environmental costs, simultaneously. Decisions entail the seismic retrofit, combined seismic and energy retrofit or complete reconstruction of building-type groups. The benefits of increased energy efficiency of the upgraded buildings are incorporated to evaluate decisions from a holistic perspective. In the second section, the model is extended to address the issue of inequitable budget allocation from a public-sector perspective. Vertical equity considerations are incorporated as an optimization constraint to distribute available resources aiming to limit the discrepancy of expected losses as a fraction of income between households across income groups. The tradeoff between equity and economic efficiency is explored. Results show that life-cycle environmental impacts constitute an informative performance metric to regional risk mitigation decision-makers, in addition to the more customarily used monetary losses. Although construction costs primarily dictate optimal decisions from an economic perspective, energy considerations largely impact optimal decisions from an environmental perspective.